The Pew Internet and American Life Project talks to Americans about their use of the Internet on an ongoing basis: Their most recent finding is that 34 percent of those surveyed have used the Internet wirelessly at home, work, or elsewhere. Their free report shows that 72 percent of wirelessly connected users check email every day, compared to 63 percent of home broadband and 54 percent of all Internet users. They also found 80 percent of wireless users have broadband at home, which makes a lot of sense.
75 percent of wireless users have accessed the Internet from at least two of the three areas surveyed: home, work, and some other place, which also correlates to anecdotally observed behavior. The report is based on under 800 respondents with just a few percentage points of expected error.